Mars

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The planet Mars is putting on quite a show. It's closest to Earth this week, so it's at its brightest. It looks like a bright orange star. And it's on display all night -- it rises around sunset, soars high across the sky during the night, and sets around sunrise.

We know more about Mars than any planet other than our own. Some of that knowledge is just the basics: it's the fourth planet from the Sun, it's a little more than half Earth's diameter, and much of its surface looks orange or gray.

But thanks to almost a score of missions to the planet, we also know a lot of the details.

We know, for example, that Mars has an atmosphere. It's about one percent as thick as Earth's, and it's made mainly of carbon dioxide. It sometimes stirs up giant dust storms that can cover much of the planet.

The Martian surface closely resembles Earth's. It has polar ice caps, big sand dunes, and mountains and valleys -- including a system of canyons that make the Grand Canyon look like something a child dug in a sandbox.

The surface also bears the scars of running water, including riverbeds and fields of boulders deposited by giant floods. Most of those scars are ancient, though -- Mars has probably been cold and dry for most of its existence.

Even so, Mars is more like Earth than any other planet in the solar system. That makes it a popular target for exploration -- a world to ponder as you watch it sail across the cold January sky.

More about Mars tomorrow.

Script by Damond Benningfield, Copyright 2009

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